1. Field of the Invention
The present invention relates to hard disk drive suspensions and, more particularly, to a method for dynamically measuring suspension in-plane and out-plane thermal drift in hard disk drives.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Typically, the magnetic heads include a write element for magnetizing the disks and a separate read element for sensing the magnetic field of the disks. The read element is typically constructed using a magneto-resistive material that has a resistance that varies with the magnetic fields of the disk. Heads with magneto-resistive read elements are commonly referred to as magneto-resistive (MR) heads.
Each head, sometimes referred to as a head slider, is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (HGA). The HGA's are attached to an actuator arm. The actuator arm has a voice coil motor that moves the heads across the surfaces of the disks.
Information is stored in radial tracks that extend across the surfaces of each disk. Each track is typically divided up into a number of segments or sectors. The voice coil motor and actuator arm can move the heads to different tracks of the disks and to different sectors of each track.
A suspension interconnect extends along the length of the flexure arm and connects the head to a preamplifier device of the voice coil motor. The suspension interconnect typically comprises conductive write traces and conductive read traces.
Data is written to the disk as the disk is rotating at a high frequency. Heat is generated as current flows along the write traces when writing data. This heat can cause the write traces to expand. Forces applied to the HGA by the expansion of the write traces can cause changes to the geometry of the flexure by causing bending or torsion of the HGA. This bending or torsion of the HGA is known as “Thermal Drift” in the art.
Thermal drift of the HGA may cause the HGA to shift in three dimensions. For example, the thermal drift of the HGA may cause the HGA to drift from a first data track towards an adjacent data track while writing data, resulting in track misalignment. This track misalignment may cause errors when the read/write heads do not properly align with tracks on the disk, adversely affecting the writing and/or reading of data. This can result in Position Error Signal (PES) errors.
Bending or torsion of the HGA may cause the head to move vertically relative to the surface of the disk, which may adversely affect reliability of the hard disk drive. For example, the vertical movement of the head toward the disk's surface may cause the head to contact the surface of the disk, which may cause damage to both the HGA and the disk, such as thermal asperity and medium surface scratching (TA/Scratch) or defects.
Vertical movement of the head away from the disk's surface may reduce the intensity of write data signals received on this disk's surface. This may adversely affect data being written to the disk and may result in data not being written to the disk.
Static thermal draft measurements have been performed in the prior art. However, results of these static thermal draft measurements are useful for reference only, due to the complexity of the dynamic head-disk interface (HDI) interaction.
Accordingly, there exists a need for a method for dynamic in-situ characterization of in-plane and out-plane suspension thermal drift in hard disk drives.